Method for hydrostatic extrusion

ABSTRACT

A billet for hydrostatic extrusion if provided near its rear end with holes therein which are left open so as to be filled by the fluid extrusion medium or are filled with a material of less resistance to deformation than the material of the billet. The billet is extruded through a conical die. When the portion of the billet containing the holes enters the die, the pressure in the pressure medium drops and in response to such drop in pressure the supply of pressure medium is stopped. The extruded portion is broken off from the unextruded part and the material in the holes escapes and this causes a noise which may also be used to indicate that extrusion should be stopped.

United States Patent [191 Aberg I Dec. 3, 1974 METHOD FOR HYDROSTATIC EXTRUSION [75] Inventor: Bertil Aberg, l-lelsingborg, Sweden [73] Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden [22] Filed: Sept. 14, 1973 [21] Appl. No.: 397,303

ll/l97l 8/1973 Primary Examiner-Richard J. l-lerbst 7] ABSTRACT A billet for hydrostatic extrusion if provided near its rear end with holes therein which are left open so as to be filled by the fluid extrusion medium or are filled with a material of less resistance to deformation than the material of the billet. The billet is extruded through a conical die. When the portion of the billet containing the holes enters the die, the pressure in the pressure medium drops and in response to such drop in pressure the supply of pressure medium is stopped. The extruded portion is broken off from the unextruded part and the material in the holes escapes and this causes a noise which may also be used to indicate that extrusion should be stopped.

11 Claims, 16 Drawing Figures &

Wy /wv/ m METHOD FOR HYDROSTATIC EXTRUSION BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to hydrostatic extrusion.

2. The Prior Art The present invention relates to a method for hydrostatic extrusion, in which a billet is enclosed in a pressure chamber in an extrusion press. The pressure chamber is filled with a pressure medium and the pressure in the pressure medium which surrounds the billet is then raised to such a level that the billet, under the influence of the pressure medium, is pressed out through an opening in a die which gives a product of the desired cross-section.

In hydrostatic extrusion it is necessary to prevent the billet from being pressed out completely since pressing the billet out completely involves an exposive outflow of the pressure medium, which may cuase damage'to the die, the pressed product and may jeopardize the safety of the personnel. Simultaneously, it is desirable that the material in the billet should be utilized to the greatest possible extent and, thus, for the extrusion to be interrupted as late as possible.

SUMMARY OF THE INVENTION remains in the pressure chamber. The invention also relates to a method of cutting off a pressed profile.

According to the invention, the billet is provided at its rear part with a cavity means by which is filled with pressure medium or another substance of less resistance to deformation than the material of the billet and which is separated from the pressure chamber at the end of the extrusion. When the cavity containing the pressure medium passes the die the die the extrusion ratio is changed, which means that the pressure necessary for the extrusion is temporarily reduced. It is possible to make the cavity so large that the pressure is re duced by more than percent, which is sufficient for the reduction to be indicated and give an output signal 1 which may be used for interrupting the extrusion. The

change of pressure is measured indirectly for a transducer which senses the pressure in the operating cylinder for the pressure-generating punch. A second effect is that the pressure medium expands when the cavity passes through the die opening and gives rise to a bang which may be detected and used as a control signal for interrupting the extrusion. A third effect is that the pressure medium bursts the pressed product when it a has passed the die opening. When the cavity is of a suitable shape and size, the pressed product can be completely broken off.

The cavity may be shaped in many ways. It may consist of one or more preferably radially drilled holes which may either be drilled so that they are separated from each other or pass completely through the billet and communicate with each other at the point of crossing in the centre of the billet. The invention can also be applied tothe extrusion of tubes. In this case a tubular billet is the starting material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows schematically a pressure chamber with an inserted billet;

FIGS. 2 to 5 show alternative embodiments of the rear end of the billet;

FIGS. 6 to 10 illustrate what happens when extruding a billet having bores according to FIG. 1;

FIGS. 11 to 15 illustrate what happens when extruding a tubular billet having radial holes drilled through the wall of the tube and;

FIG. 16 shows a time-pressure curve for the pressure chamber or the operating cylinder for the pressuregenerating punch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the figures, l designates a part of a stand in an extrusion press, the rest of which is not shown. In the press is a high pressure cylinder 2 which forms a closed pressure chamber 5 together with a die 3 projecting into the cylinder 2 and a pressure-generating punch 4. Between the cylinder 2 and the die 3 and the pressuregenerating punch 4 there are seals 6 and 7, respectively. A billet is inserted into the pressure chamber 5. The pressure chamber 5 is filled with a pressure-medium, normally castor oil. The forward, pointed part 9 of the billet 8 seals against the conical inlet opening 10 of the die 3. The billet 8 is provided at its rear part with a number of drilled holes 11 which do not communicate with each other. These holes are naturally filled with the pressure medium from the pressure chamber. In the embodiment according to FIGS. 2 and 3 the billet is provided with two drilled holes 12 passing through the billet which communicate with each other at the crossing point in the centre of the billet. FIGS. 4 and 5 show an embodiment in which an annular slot 21 forms the cavity which is filled with pressure medium.

FIGS. 6 to 10 show the extrusion of the last part of a billet 8 having a number of radial holes 11. A bar 14 has been shaped in the die opening 13. Before the radial plane, where the holes 11 are located, reaches the inlet cone 10 of the die, the holes communicate with the surrounding space in the pressure chamber 5, as shown in FIG. 6. When the area in question has reached and entered the inlet cone 10, as shown in FIG. 7, the drilled holes are separated from the pressure chamber by the wall in the inlet cone. When the billet is further extruded and the billet part with the holes 11 are pressed down into the cone 10, the depth of the holes 11 is reduced. The constant volume of the enclosed pressure medium expands the hole in a manner shown in FIGS. 8 and 9. When the holes 11 pass through the die opening 13, the pressure medium enclosed in the holes flows out and is able to tear off the bar 14 when the holes 11 are suitably dimensioned. In this way a cone of the pressed profile can be obtained.

FIGS. 11 to 15 shows the last part of the extrusion of a hollow billet 16, in which a tube 17 is formed in the gap between the opening 13 in the die 3 and a mandrel 18. In the billet 16 are drilled holes 19 which open out into the holes 20 of the billet 16. FIGS. 11 to 15 correspond essentially to FIGS. 6 to 10. A detailed description is therefore not necessary.

When the notches of the billets 8 and 16, respectively, with the holes 11 and 19, respectively, enter the inlet cone 10, the extrusion ratio is reduced and the pressure falls in the pressure chamber 5 and in the op erating cylinder of the punch 4. The development of pressure in the extrusion is illustrated in FIG. 16. The extrusion pressure increases from P O to P, after the time At the pressure P, the extrusion of a rod 14 and a tube 17, respectively, is started. After this the pres sure falls a little to the value P and remains substantially constant until the holes 11 and 19, respectively, enter the inlet cone at the time t The pressure then falls to the value P This change of the pressure is indicated by a transducer, and an output signal from this transducer is utilized for interrupting the extrusion by interrupting the supply of pressure medium to the operating cylinder of the punch 4. When the pressure medium enclosed in the holes 11 and 19, respectively, flows out through the die opening 13 (See FIGS. 10 and 15) a bang is obtained which can also be utilized as a signal for interrupting the extrusion.

The holes drilled into the billet can also be filled with a solid material which gives less resistance to deformation than the material of the billet. Plastic plugs, for example, can be inserted into the holes 11 and 19, respectively.

I claim:

1. Method for hydrostatic extrusion, which comprises enclosing a solid billet in a pressure chamber in an extrusion press, surrounding the billet by a pressure medium, raising the pressure in the pressure medium to such a level that the material in the billet, under the influence of the pressure medium, is pressed out through an opening in a die which gives a product of the desired cross-section, in which the billet at its rear part is provided with cavity means opening in the side wall of the billet which communicates directly with the pressure medium during the greater part of the extrusion and which is filled during the extrusion with a material having less resistance to deformation than the material of the billet.

2. Method according to claim 1, in which the die has a conical inlet opening and the cavity means opens in the exterior side surface of the billet, whereby engagement of the mouth of the cavity with the walls of the inlet opening seals the cavity from the pressure chamber near the end of the extrusion.

3. Method according to claim 1, in which the cavity means comprises at least one hole extending from the side surface of the billet into the interior thereof.

4. Method according to claim 3, in which the cavity means comprises radially directed holes in the billet.

5. Method according to claim 4, in which the holes communicate with each other.

6. Method according to claim 1, in which the cavity means comprises an annular groove in the billet.

7. Method according to claim 6, in which the billet has a conical point and the groove is located at a distance from the rear end of the billet more than onethird of the length of the conical point.

8. Method according to claim 1, which comprises interrupting the supply of pressure to the pressure chamber in response to the exit of the cavity means from the die.

9. Method according to claim 1, in which a bang occurs when the pressure medium enclosed in the cavity means flows out through the die opening which comprises interrupting the supply of pressure medium in response to the bang.

10. Method according to claim 1, in which the cavity means is filled with a solid material having less resistance to deformation than the material of the billet.

11. Method according to claim 1, in which the pressure medium enclosed in the cavity cuts off the expressed product because of its expansion when the cavity means passes through the die opening. 

1. Method for hydrostatic extrusion, which comprises enclosing a solid billet in a pressure chamber in an extrusion press, surrounding the billet by a pressure medium, raising the pressure in the pressure medium to such a level that the material in the billet, under the influence of the pressure medium, is pressed out through an opening in a die which gives a product of the desired cross-section, in which the billet at its rear part is provided with cavity means opening in the side wall of the billet which communicates directly with the pressure medium during the greater part of the extrusion and which is filled during the extrusion with a material having less resistance to deformation than the material of the billet.
 2. Method according to claim 1, in which the die has a conical inlet opening and the cavity means opens in the exterior side surface of the billet, whereby engagement of the mouth of the cavity with the walls of the inlet opening seals the cavity from the pressure chamber near the end of the extrusion.
 3. Method according to claim 1, in which the cavity means comprises at least one hole extending from the side surface of the billet into the interior thereof.
 4. Method according to claim 3, in which the cavity means comprises radially directed holes in the billet.
 5. Method according to claim 4, in which the holes communicate with each other.
 6. Method according to claim 1, in which the cavity means comprises an annular groove in the billet.
 7. Method according to claim 6, in which the billet has a conical point and the groove is located at a distance from the rear end of the billet more than one-third of the length of the conical point.
 8. Method according to claim 1, which comprises interrupting the supply of pressure to the pressure chamber in response to the exit of the cavity means from the die.
 9. Method according to claim 1, in which a bang occurs when the pressure medium enclosed in the cavity means flows out through the die opening which comprises interrupting the supply of pressure medium in response to the bang.
 10. Method according to claim 1, in which the cavity means is filled with a solid material having less resistance to deformation than the material of the billet.
 11. Method according to claim 1, in which the pressure medium enclosed in the cavity cuts off the expressed product because of its expansion when the cavity means passes through the die opening. 